It is common practice in agriculture to dispense plant protective agents onto plant sites using tractor-born equipment, such as sprayers or other dispensing apparatus The plant-protective agents which may be applied can include fertilizers, weed-suppressing herbicides, insecticides, fungicides, growth promoting or growth suppressing hormones, chemicals and biological agents, and the like.
Since such agents may be detrimental to the health of the operator, generally the ventilation system of the tractor cab was provided with a special filter in the hope of removing toxic or other potentially dangerous or noxious substances before the ventilating air reached the operator.
For the most part such filters were comprised mainly of active carbon or active coal.
However, the spectrum of plant-protective agents is so wide and the compositions which are dispensed onto the plant site and which may be entrained in the ventilating air are so diverse that frequently a single filter was unsatisfactory and could not insure complete removal of all of the detrimental substances. Of course, specially designed filters have not been fully developed for all plant-protective agents and are not always reliable. Furthermore, they may be very costly and may require constant monitoring.
Measuring devices for the continuous monitoring of such filters to insure that the activity of the filter will be substantial for all types of agents are expensive and technologically complex so that widespread use of such systems cannot be expected and is scarcely possible.